In a semiconductor-device manufacturing process, in order to fill holes between electric wirings formed on a semiconductor wafer as an object to be processed, or in order to provide barrier layers, a metal such as Ti, Al or Cu and/or a metal compound such as WSi, TiN or TiSi is deposited to form a thin film.
Conventionally, such thin film of the metal or metal compound is deposited by means of physical vapor deposition process (PVD). However, recently, it is requested to make devices micro and highly integrated, so that design-rule is especially severe. Thus, it is difficult to obtain sufficient properties by PVD, which is inferior in filling performance. Then, such thin film starts to be deposited by CVD, which we can expect forms a film of better quality.
As a conventional CVD film-forming apparatus, an apparatus for forming a Ti film is explained as an example. In the CVD film-forming apparatus for forming a Ti film, a pedestal, in which a heater is embedded and onto which a semiconductor wafer is placed, is arranged in a chamber having another heater. A showerhead for discharging a process gas is provided above and opposite to the pedestal. The chamber is heated to a predetermined temperature, and the inside of the chamber is vacuumed to a predetermined vacuum level. Then, the semiconductor wafer placed on the pedestal is heated to a predetermined temperature, while the process gas such as TiCl4, H2 and the like is supplied from the showerhead. In addition, a high-frequency electric power is applied to the showerhead, so that the process gas is changed to plasma thereof. Then, the film-forming process is conducted.
However, recently, the semiconductor wafer starts to be enlarged to 300 mm. Thus, the film-forming apparatus has to be enlarged correspondingly. Therefore, the following problems appear manifestly.
When the temperature of the heater embedded in the pedestal rises up, the showerhead provided opposed to the pedestal is heated by radiant heat thereof. However, when the unit is enlarged, the showerhead is also enlarged, that is, heat capacity thereof becomes larger, so that it takes a longer time for the temperature to become stable when the showerhead is heated. That is, the throughput is deteriorated. If the temperature of the showerhead, that is, the surface temperature of the showerhead is not stable during a process, the process is not uniformly conducted. In addition, the conventional showerhead has a structure with high heat-insulating properties, in order to secure temperature stability during a process. Thus, if the showerhead is enlarged, it takes also a longer time to lower the temperature to a predetermined temperature, for example for a cleaning process. If the cleaning process is conducted under a high-temperature state, the showerhead member may be damaged.
In addition, during an idling state, the temperature of the pedestal has to be set higher than that during the process, in order to maintain the temperature of the showerhead at a predetermined temperature. This is explained in detail. Conventionally, during the plasma process, the temperatures of members in the chamber are raised by the plasma. Especially, the surface temperature of the showerhead tends to be raised because it has a large area opposed to the wafer surface and exposed to the plasma. However, when a film-forming process is conducted after an idling state or a cleaning process, it is possible that a film-forming rate for the first wafer is low. It is thought that the reason is that the temperature of the showerhead is low. That is, the temperature thereof is about 500° C. during a normal film-forming process, but it is thought that the temperature falls down by about 20 to 30° C. In order to prevent this, during the idling state or the cleaning process, the temperature of the pedestal had to be set higher than the film-forming temperature.
Furthermore, conventionally, at a maintenance process of the showerhead, an upper lid including the showerhead is opened by a degree not larger than 90 degrees, and then the showerhead is removed or the like. However, as the film-forming apparatus is enlarged, when the showerhead is also bulked or enlarged, it is difficult to conduct the maintenance process of the showerhead in accordance with the conventional method.